The present invention relates to a crucible cover for vacuum coating installations with an electron beam source acting as the energy source, and a pivotable or rotatable crucible having several material pockets. The cover covers the material pockets which are not to be heated by means of the energy source during at least one phase of the coating process.
In known vacuum coating methods, as for example by means of thermal vaporization by electron beam guns, the objects to be coated are introduced into a vacuum chamber. In installations for applying different layers in the same process, this vacuum chamber contains a crucible with several material pockets holding the various materials. Such a device is known from Swiss patent No. 663,037 where the crucible is installed in the device, or respectively in the source, in such a way that rotary or pivoting movements of the crucibles are possible. This makes it possible to bring the pocket containing the coating material into the desired position for vapor deposition. Cooling devices are also present as well as energy sources or electron beam sources for melting and vaporizing the coating material in the desired material pocket. When applying several layers of different materials successively on the objects to be vapor-treated in such an apparatus, for example in the production of electronic chips, the vacuum chamber must not be opened before the end of the treatment process. Otherwise uncontrolled reactions will result in the interface regions between the individual layers, and the vacuum conditions will no longer comply with the requirements of the process. This results in unusuable products of very expensive substrates. In these processes crucibles are used which contain two, three, four or more material pockets, each of which may be filled with a different coating material. The pockets whose content is not being vaporized must be covered during the process, to avoid contamination of their content with the coating material being processed.
From Swiss patent document CH 663,037-A5 (U.S. Pat. No. 4,748,935) the use of a cover is known to protect against contamination of those parts of the crucible which are not needed during a certain process step. These known covers are fixed and lowered onto the surface of the crucible or the pockets as close as possible, to prevent contamination. With the use of highly dispersive coating materials, such as gold, or in the case of large crucible volumes, the danger of so called "cross-talk" or cross-contamination between pockets is increased, owing to which further contamination occurs. This is not desired if especially stringent requirements are set for coating quality. Highly dispersive materials may also interfere with the succession of movements of the crucible. These interferences are attributable to the fact that in the gap zones between the cover and the crucible as well as the pockets, material deposits which is vaporized in the instantaneous coating process and, after a certain time, movement of the crucible can no longer be carried out. As a result, the vacuum chamber must be vented to be able to clean the crucible and the cover, so that on the one hand interruptions of operations result and on the other hand the quality of the substrates being processed in the vacuum chamber can no longer be guaranteed. The substrates must be treated as scrap, resulting in very high losses, since in most cases very expensive objects are involved.